1. Field of the Invention
The present invention relates to an optical fiber wiring board for optically connecting optical elements, optical circuits or optical devices to each other.
2. Description of the Related Art
Improvement of transmission rate has been intended in the inside of communication apparatus and computers in recent years. Examination of optical interconnection substituted for electric wiring heretofore used has been advanced for high-rate transmission. At present, a proposal has been made on an optical fiber wiring board in which a large number of optical fibers are arranged as wiring in a backboard or in a plug-in unit so as to be integrated into the form of a board. Such an optical fiber wiring board generally is formed as follows: A large number of optical fibers are arranged as wiring on a sheet-like substrate provided with an adhesive layer. Then, at least one optical fiber is led out at a predetermined position from an edge portion of the substrate. When a plurality of optical fibers are led out at the predetermined position, they are led out in a condition that they are horizontally arranged in a row. Finally, connectors are attached to the ends of the optical fibers thus led out.
As a structure of leading out the optical fibers, a following configuration has been disclosed in Japanese Patent No. 2574611. That is, tab portions in form of protrusion portions are provided on optical fiber leading-out portions of the substrate so that optical fibers are extended out along the tab portions. In this configuration, the optical fiber leading-out portions can be mechanically reinforced with the tab portions. Moreover, the optical fibers extended out from the substrate can be pulled around when the tab portions are curved in a direction vertical to the plane of the substrate or twisted. Therefore, there is an advantage that degree of freedom in points of connection of connectors is increased.
In the configuration, the degree of freedom for curving the tab portions in a direction vertical to the plane of the substrate is obtainable. However, the tab portions cannot be curved in a left-right direction with respect to a direction in which the tab portions are protruded out from the substrate because the tab portions protruded out from the substrate are formed integrally with the substrate. There is a disadvantage that the degree of freedom is limited when optical fibers are pulled around from the optical fiber leading-out portion in a direction horizontal to the plane of the substrate and connected by connectors connected thereto. Further, the tab portions are twisted so that the optical fibers can have the proper orientation with respect to a direction in which the optical fibers are led out. That is, the optical fibers themselves are twisted along the optical fiber leading-out direction by at a predetermined angle, so that orientation of the connecters connected to the optical fibers can be adjusted so as to match with connectors connected to an equipment to be mounted (hereinafter referred as equipment-side connectors). However, since the tab portions are formed integrally with the substrate, the degree of freedom allowed to twist the tab portions is limited. For example, it is difficult to twist the tab portions at 90xc2x0 or 180xc2x0 relative to a body portion of the substrate. Further, there is a disadvantage that the optical fibers cannot be maintained in the twisted shape. Moreover, when the optical fibers are maintained in the twisted shape over a long period of time, since the optical fibers themselves are twisted substantially, the stress depending on the elasticity of optical fibers is applied on end portions of the optical fibers or base portions of the tab portions. Particularly, when the optical fibers are led out in the condition that a plurality of optical fibers are horizontally arranged closely to one another in a row, the degree of freedom allowed to bend the optical fibers in the left-right direction or twist the optical fibers without increase of loss or damage in the optical fibers in the extension portion is limited extremely.
Therefore, an object of the invention is to provide an optical fiber wiring board having an optical fiber leading-out structure in which a bundle of optical fibers led out from a substrate can be pulled around freely in a direction horizontal to the plane of the substrate as well as in a direction vertical to the plane of the substrate, in which the optical fibers are freely orientated with respect to a direction in which the optical fibers are led outs and in which the optical fibers extended out from the substrate can be mechanically reinforced sufficiently.
In order to accomplish the object above, the following means are adopted. According to the invention, there is provided an optical fiber wiring board comprising: a substrate; a plurality of optical fibers arranged as wiring on the substrate; and extension portions, each including a base portion having a predetermined length front an edge portion of the substrate, and a forwarding end portion connected to a side of the base portion opposing the substrate; wherein each of the extension portions also includes some optical fibers disposed adjacent to one another, wherein the some optical fibers at the base portion are not fixed relative to one another whereas the some optical fibers at the forward end portion are fixed relative to one another integrally.
In the optical fiber wiring board, it is preferable that the some optical fibers in each of the extension portions are led out from the substrate closely to one another in a row in a horizontal direction, and wherein the some optical fibers at the forward end portion are integrated so that the some optical fibers are arranged adjacent to one another in a row. Preferably, the optical fibers at the forward end portion maybe integrated so that the some optical fibers are aligned in a tape-like shape and wherein the integrated optical fibers at the forward end portion may be aligned non-parallel to the substrate.
In such a configuration, a bundle of the optical fibers at the base portion can be curved freely because the optical fibers at the base portion are not fixed to one another but made free. Accordingly, the optical fibers led out from the substrate can be pulled around freely in directions horizontal and oblique to the plane of the substrate as well as in a direction vertical to the plane of the substrate. On the other hand, the bundle of the optical fibers at the forward end portion is not separated into pieces because the optical fibers at the forward end portion are integrally fixed relative to one another, for example, to form a tape-like shape. Moreover, the state of arrangement of the optical fibers in the portion in which the optical fibers are led out from the substrate is not disordered.
Further, in the optical fiber wiring board, it is preferable that the optical fibers at the forward end portion are integrated so that the some optical fibers are aligned in a tape-like shape and aligned non-parallel to the substrate while each of the optical fibers is not twisted about its center axis.
In such a configuration, a bundle of the optical fibers at the base portion can be curved freely because the optical fibers at the base portion are not fixed relative to one another but made free. Accordingly, the optical fibers led out from the substrate can be pulled around freely in directions horizontal and oblique to the plane of the substrate as well as in a direction vertical to the plane of the substrate. Further, in the extension portions, the proper orientation of the optical fibers is maintained because the optical fibers at the forward end portion are integrated so that the some optical fibers are aligned non-parallel to the substrate while each of the optical fibers is not twisted about its center axis is maintained. Therefore, even if the orientation of connectors of optical fibers need to be adjusted in accordance with the equipment-side connectors, the optical fiber wiring board can be easily mounted on the equipment to be mounted. That is, when the connectors of optical fibers are connected with the equipment-side connectors in such a condition that they have an angle relative to the plane of the substrate, the connectors of the optical fibers can be easily connected with the equipment-side connectors.
The above-mentioned optical fiber wiring board preferably further comprises a protective tube protecting at least at the base portion of each of the extension portions; and a lock portion provided in the edge portion of the substrate for locking one end portion of the protective tube relative to the substrate. In this case, preferably, the lock portion includes notch portions formed at portions in the substrate, between which the some optical fibers are extended out from the edge portion of the substrate, wherein the one end portion of the protective tube is fitted and locked to the notch portions. In this configuration, the base portion is protected by the protective tube, so that the mechanical strength of the base portion can be reinforced in a state in which the bundle of optical fibers is separated into pieces. Hence, damage can be avoided when the optical fibers led out are pulled around.
Further, the above-mentioned optical fiber wiring board, preferably further comprises a skin layer covering the forward end portion of each of the extension portions: a first protective tube for protecting at least the base portion of each of the extension portions; a second protective tube for covering the first protective tube and covering an exposed portion of the plurality of optical fibers reaching the skin layer; and a lock portion provided in the edge portion of the substrate for locking one end portion of the first and second protective tubes relative to the substrate. In this configuration, there is an advantage that the optical fiber leading-out portion can be protected over the whole length by the second protective tube in accordance with the outer diameter of the skin layer. Moreover, there is an advantage that the base portion can be protected by the first protective tube.
A heat-shrinkable tube is preferably used as the protective tube. In this case, the heat-shrinkable tube may be heat-shrunk after one end portion of the heat-shrinkable tube is fitted into the lock portion of the substrate. After heat shrinking, the tube is made thin in the portion locked to the substrate. Hence, a level difference between the tube and the substrate is reduced. Moreover, the adhesive property between the inside of the tube and the substrate/optical fiber is made good. Hence, tolerance to dropout is preferably improved.